Which of the following cations will turn a borax bead green in an oxidising flame? — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

Step 1: The brown ring test for nitrate ions results in the formation of a brown coordination complex. Step 2: The brown complex has the formula [Fe(H2O)5(NO)]2+. In this complex, nitric oxide transfers an electron to Fe2+ to become NO+, reducing the iron to a +1 oxidation state (Fe+). Step 3: Therefore, the oxidation state of Fe in the brown ring complex is +1, which corresponds to option (b).